The origins of individual differences in blood pressure sensitivity to high salt intake and its role in the development of chronic hypertension remain to be clarified. Increased incidence of salt sensitivity has been observed in older persons, blacks and hypertensives. It is known that the rate of increase in blood pressure with age in women is less than that of men before menopause, but greater afterwards. The first objective of this study is to confirm that blood pressure sensitivity to salt intake in postmenopausal women is a function of their resting "breathing pattern", as we previously found in older women. The second objective of this proposal is to determine whether estrogen administration decreases blood pressure sensitivity to high salt intake in postmenopausal women. The final hypothesis is that the extent of the effect of estrogen administration on blood pressure sensitivity to high salt intake will be a function of the individual aygmentation of nitric oxide metabolism.